Page 280 - Fundamentals of Magnetic Thermonuclear Reactor Design

Plasma Control System Chapter | 8 259

One of the most advanced codes for accomplishing these aims is the DINA
code, developed in Russia [3]. DINA allows accounting in a self-consistent
manner for
l 2D free boundary plasma equilibrium
l 1D transport processes for plasma parameters averaged over magnetic flux
surfaces.

The vacuum vessel is described by a set of axisymmetric filaments. Cur-
rents in the vessel and poloidal field coils are computed self consistently
with the evolution of plasma. 2D equilibrium equations are solved with a
combination of the conventional finite element method and the variable in-
version technique. The transport processes are described by equations for
plasma components (H, D, T), electron and ion temperatures and poloidal
magnetic flux diffusion. Current drive and bootstrap current models, neutral
beam injections (set of filament-like beams), as well as injection of pellets
that evaporate fast compared to τ have all been included in the DINA code
Е
as subroutines.
The code also factors in the effect of eddy currents in the vessel shells on the
plasma column evolution. DINA allows modelling the plasma current position
and shape control system.
Let us consider the stage-by-stage simulation of a control system at the non-
linear modelling of discharge scenarios [4]. The stage-by-stage approach is also
feasible when planning an experiment.
At the first stage, we select preprogrammed (target) parameters to be con-
trolled by feedback loops. For limiter-phase plasma configurations during
the current ramp-up and plasma termination phases, these may include the
following:

l Velocity of vertical displacements for the stabilisation of the plasma’s verti-
cal instability by the fast control loop. For example, vertical displacement
time in ITER is 70–200 ms.
l Plasma vertical position (a ‘slow’ plasma shape control loop). For ITER, the
time is a few seconds.
l Gap between the first wall and the point on the plasma boundary with in-
nermost or outermost radius (the ‘slow’ plasma shape control loop).
l Currents in poloidal field coils (the ‘slow’ loop).
l Plasma current (the ‘slow’ loop).
For divertor-phase plasma configurations during the current ramp-up, flat
top and plasma termination phases, these may include the following:
l Velocity of vertical displacements for the stabilisation of the plasma’s verti-
cal instability by the fast control loop.
l Gaps between the first wall and the points on the plasma boundary mainly
affecting the plasma performance (the ‘slow’ plasma shape control loop).